Positive displacement hydraulic pumps

ABSTRACT

This invention presents several configuration of a new positive displacement pump with variable geometric volume for hydraulic drive and control system or else, this pump consists of one more pumping groups. When one pumping group is used an external energy storage system is to be utilized. This is not necessary in the case when the pump has two or more pumping groups. 
     A pumping group consists of a cam that pushes one or more followers, which encircle the cam to form enclosed chamber. During the cam rotation the followers rise and fall. During the followers rise, the encircled volume between the cam and the followers expands, and sucks oil. The rising followers push control oil that exists in a control chamber behind them. In a pump with more than one pumping group, e.g. two pumping groups, this control oil is fed to the control chamber of the other pumping group, with followers in opposite phase with respect to those of the first pumping group. The second pumping group followers thus are pushed to fall towards their cam. The falling followers contract the encircled chamber to cause the discharge stroke of the second group. By controlling the control oil volume flowing between the two groups, the stroke of the followers is controlled and hence the pump geometric volume is controlled. The followers can be rigid components which slide relative to each there, or alternatively flexible.

TECHNICAL FIELD

Positive displacement pumps are used to convert the mechanical power generated by prime movers to hydraulic power. In hydraulic drive and control systems, the hydraulic power is controlled and transmitted to hydraulic actuators where it is converted to mechanical power again to move bodies against external loads in controlled motions. Moreover, pumps are used in a wide range of applications such as lubrication and fluid transfer.

BACKGROUND ART

Hydraulic drive and control systems are characterized by their large transmitted power density when compared with many other systems. They can provide large forces/torques by small actuators. As control systems, they can provide accurate, fast and precise control of motion or forces/torques. On the other hand, these systems are generally not as efficient or economic as many other systems.

To control a motion of an actuator, the hydraulic power generated by the pump is controlled and used to drive this actuator. The control of hydraulic power can be realized either by controlling the pump geometric volume or by using control valves. Controlling the hydraulic power directly by controlling the pump is the most efficient way, but in most applications this method of control cannot comply with all the control requirements. This is because the pump dynamic behavior in most cases does not meet the required high system performance. Besides, the pump in this case can't control more than one actuator simultaneously. When using valves to control the actuator motion, the required high performance can be realized, but because the valves are essentially throttling devices, this control method is characterized by high power losses and low efficiency.

DISCLOSURE OF INVENTION Technical Problem

In hydraulic control systems the best choice is to use a pump with variable geometric volume directly to control the actuator. Controlling actuators directly by means of a variable geometric volume pump has drawbacks. In this method of control the pump cannot control several actuators simultaneously. Besides, the dynamic response of the bulky pump geometric volume control mechanism negatively affects the response of the whole system. When using control valves to control actuators, the control of the pump geometric volume is commonly used when a system with high efficiency is required. From an economic point of view, the many precise pump control components make the pump in most cases complicated and costly in production, operation and maintenance. In applications rather than fluid power control such as lubrication and fluid transfer, simple and compact pumps provide economic solutions for such applications.

In this invention, these problems are considered. In the invented pump, only a small amount of control oil is used to control the pump geometric volume, and a small change in this control oil volume is sufficient to produce the required change in the pump geometric volume. In this way, the bulky control mechanism mechanical components are eliminated, and consequently the production costs are reduced. The small change in the volume of control oil which produces sensible change in the pump geometric volume improves considerably the pump dynamic characteristics. The pumping groups in this invention, being simple and compact, provide design flexibility to assemble many pumping groups on one drive shaft to form one pump, capable to drive and control several actuators in the same time. These advantages are still valuable for pumps of constant geometric volume.

Solution to Problem

The invented pump might have one or more pumping groups. When one pumping group is used an external energy storage system is to be utilized. This is not the case when the pump has two or more pumping groups. A pumping group consists of a cam that pushes one or more followers, which encircle the cam to form enclosed chamber. During the cam rotation the followers rise and fall. During the followers rise, the encircled volume between the cam and the followers expands, and sucks oil. The rising followers sweep control oil that exists in a control chamber behind them. In a pump with more than one pumping group, e.g. two pumping groups, this control oil is fed to the control chamber of the other pumping group, with followers in opposite phase with respect to those of the first pumping group. The second pumping group followers thus are pushed to fall towards their cam. The falling followers contract their encircled chamber to cause the discharge stroke of the second group. By controlling the control oil volume flowing between the two groups, the stroke of the followers is controlled and hence the pump geometric volume is controlled. Pushing the followers towards the cam can be realized also from an external pressure source of a pressure higher than the pump delivery pressure, spring or mechanism. Besides, the invention presents possible techniques for pushing the followers towards the cam during the delivery stroke against the high delivery pressure using the possibly lower control oil pressure in case of to providing this control oil from the pump own discharge. This is necessary to avoid using an external pressure source for control oil feeding. The first technique is to make the followers from flexible elements to act as springs. By proper design and selection of these springs and their pre-loading, their contraction force would be added to the control oil pressure force in order to overcome the discharge pressure. The second technique is by applying the lower control oil pressure to a follower area larger than the follower area subjected to the higher discharge pressure. This can be realized by forming buckets connected to zero pressure between the follower segments.

In order to reduce the contact stresses between the cam and its followers a proper design of the curvatures at the contact zone should be made. Alternatively the contact force would be distributed between fixed and rolling elements or adding pads.

In hydraulic drive and control systems positive displacement pumps are used to transfer the available mechanical power to hydraulic power. In these positive displacement pumps enclosed volumes expand and contract during each pump shaft rotation, suck oil inside these volumes during their expansion, then deliver the sucked oil to the pump discharge line during contraction process.

FIG. 1 shows the main parts of the invented pump which has a housing (2). The pump has one shaft (1) that carries two cams (12) and (22), but the cams are shown in split representation to explain the functionality of the components. The cams are set out of phase with respect to each other. The cams rotation causes the followers (13) and (23) to move outwards and inwards with respect to the cams. Rollers (14), or else, can be inserted between the cams and the followers to distribute the interacting loads between the cam and the followers over many contact points and to provide rolling contacts instead of sliding ones. When the followers presented in the left side pumping group for instance move outwards, the volume (15) enclosed between the followers (13) and the cam increases causing oil (6) to be sucked inside this volume from tank through the check valves (17). During this phase the volume (16) of the control chamber between the followers (13) outer surfaces and the housing (2) decreases causing control oil (10) to flow to the control chamber (26) of the other pumping group. Since the cam (22) is out of phase with respect to the cam (12), the cam (22) would not in this instant push the followers (23) outwards. It would rather be moving away from them. The control oil (10) reaching the chamber (26) would now push the followers (23) towards the cam (22). This causes the volume (25) to decrease and the oil existing in this volume is discharged (7) through the valves (28) to the pump delivery port. The guides (3) shown in the figure are used to guide the followers during their motion.

During the outward motion of the followers, buckets (9) are formed. These buckets are connected to the tank line for pressure inside them to be zero. This allows the control oil pressure, which might be less than or equal to the pump delivery pressure, to push the followers towards the cam causing the pump discharge due to ratio of the areas subjected to each of them. In this way the pump delivery oil can provide the required control oil (10). Tongue (8) acts as a guide for the relative motion between the followers.

Since the sum of the volumes (15) and (16) in a pumping group is constant and equals the sum of the volumes (25) and (26) in the other pumping group, an increase of volume (15) during the suction process produces a corresponding decrease in the volume (16), and a corresponding decrease of volume (25). This means that the oil discharged volume from the volume (25) equals the volume sucked in chamber (15). With shaft rotation the two pumping groups exchange the explained actions. In this way, the suction and delivery processes occur successively from the two pumping groups. The geometric volume of a pump with two pumping groups can be seen to be proportional to twice the volume of the oil transferred between the two pumping groups during one pump shaft rotation. In the case shown in FIG. (1), the geometric volume equals the oil volume transferred from the first pumping group to the second one during one outward stroke of the followers (13), multiplied by the followers outer and inner surfaces area ratio, multiplied by 2 which is the number of the pumping groups, and multiplied by the number of outward strokes of the followers (13) during one shaft rotation, which is 3 in this case.

By controlling the value of the control oil volume transferred between the groups, the pump geometric volume can be controlled. An oil volume V, taken from this transferred control oil or added to it causes a decrease or increase of the pump geometric volume equal to V, multiplied by the followers surfaces area ratio multiplied by the number of pumping groups and the number of followers suction strokes per one shaft rotation.

FIG. (2) shows a representative view for a pumping group at its minimum volume, where all the rollers are adjacent to each other and the buckets between the followers are closed.

FIG. (3) shows a close view for two adjacent followers when they are fully contracted. The lips (31) are used to minimize the leakage to the buckets that are, connected to the tank. The bridges (32) at the ends of the followers are made to prevent the rollers (14) from dropping into the cavity formed when the followers move away from this position. The figure shows also the rollers bearings (33).

FIG. (4) shows the followers in a position away from the fully contracted position.

Other pump configurations are shown in FIGS. from 5 to 18 in which the followers are made from an elastic material, to work as springs and are made either as one or several pieces. In these configurations the followers are firmly fixed from one end for the curvature at this end to be nearly constant during operation. This ensures smooth engagement at the start of contact between the followers and the cam.

FIG. (5) shows a proposed pumping group with flexible follower. In this figure the follower (13) is shown fully contracted. The follower (13) is one flexible piece fixed from one end (34). The eccentric circular cam (12) pushes the follower through rollers (14) of radii nearly equal to the radius of curvature of the follower.

Since the deflections of the follower during cam rotation might not produce enough inner volume change, and consequently enough value for the pump geometric volume, the follower is allowed to move through the sliding block (35) and the arm (36).

FIG. (6) shows the pumping group, with the follower pushed by the cam to its extreme outer position. In this position, the oil sucked in volume (25) is maximum and the control oil volume (26) is minimum. The arm (36) serves to compensate for the follower length variation and to act as an additional support for the follower to allow increasing the suction volume of the pumping group.

In FIG. (7) another version of the pumping group is shown, with the arm (36) curved which allows getting rid of the sliding block (35) shown in the design in FIGS. 5 and 6.

In the pumping group shown in FIG. (8) the follower shape is modified so as to get rid of the arm (36) shown in FIG. (7)

FIGS. (9) and (10) depict a pumping group having two pumping actions during each revolution of the drive shaft. FIG. (9) shows the pumping group at the start of a suction process while FIG. 10 shows this group at the end of the suction process.

FIG. (11) shows a different pumping group configuration in which two pumping cambers are formed by means of one follower (13). One cam (12) actuates a part of the follower, which actuates its other part around the hinge (44).

FIG. (12) shows a pumping group similar to that shown in FIG. (11), but having two pumping actions during one drive shaft revolution. In this case arms (36) are used.

FIG. (13) shows another pumping group in which the arms and joints are replaced by flexible parts. In this configuration one pumping action is performed during each drive shaft ration. This allows the use of a roller/ball bearing with the cam. Two pumping actions can be performed during one drive shaft revolution in this case with the layout shown in FIG. (14). In this configuration, the follower is split at the positions (55) to permit the volume change during suction and delivery. The groves (56) introduced in the side plates of the pumping groups are introduced to allow free flow between the pumping chambers.

The configuration shown in FIG. (15) is characterized by inserting rollers (27) between the cam and the follower for the contact to be rolling contact instead of sliding and for distributing the forces between the cam and the follower on several points.

FIG. (16) shows the details of the split zone, with the details of separation (25) enlarged. The side view of this zone is also shown. Since the two halves separate at this zone with the cam rotation, a bridge (32) from one of them is made to extend in gap in the other so that the rollers roll on this bridge when crossing this zone without dropping in the formed gap.

BRIEF DESCRIPTION OF DRAWINGS

FIG. (1) shows the pump main parts.

FIG. (2) shows a pictorial view of a pumping group.

FIG. (3) shows the details of the zone in which separation between the followers occur.

FIG. (4) shows more details of the zone of followers separation.

FIG. (5) shows an example for a pumping group having one flexible follower and a cam with a roller/ball bearing, the group at this figure is at the start of the suction process.

FIG. (6) shows the pumping group of FIG. (5) at the end of the suction process.

FIG. (7) shows the pumping group configuration in FIGS. (5) and (6) with the slider eliminated.

FIG. (8) shows the pumping group configuration in FIG. (7) with the follower made of one flexible piece. The pump is at the start of the suction stroke.

FIG. (9) shows the pumping group presented in FIG. (6) when two pumping actions are to be performed during one shaft revolution. The pump is shown at the start of the suction strokes.

FIG. (10) shows the pumping group in FIG. (9) at the end of the suction shake.

FIG. (11) shows the pumping group with a follower made from a flexible material as one piece formed such that parts of it are turned on each other.

FIG. (12) shows the pump pumping group presented in FIG. (11) with two pumping actions performed during one shaft rotation.

FIG. (13) shows a version of a pumping group with a flexible follower made as one piece of three compartments to reduce the induced stresses.

FIG. (14) shows a pumping group as shown in FIG. (13) with two pumping actions performed during one shaft rotation.

FIG. (15) shows the pumping group shown in FIG. (14) with rollers added between the cam and the follower.

FIG. (16) shows the details of the zone of separation between the two sides of the follower and the rollers.

INDUSTRIAL APPLICABILITY

This invention presents a new hydraulic positive displacement pump with variable geometric volume. It can be used in the hydraulic power supply units of the machines and equipment which utilize hydraulic power for drive and control purposes. Hundreds of millions of these machines and equipment are running all over the globe. It can also be used for lubrication and fluid transfer pumps and all similar applications.

This invented pump is of smaller weight and volume, of lower production cost, and of higher dynamic performance when compared with the equivalent other types of pumps. Consequently it would replace many of the pumps that are used nowadays in hydraulic power supply units. Examples of the fields of application of this pump are the heavy industries, plastic processing machines, machine tools, presses, military equipment and machines, earth moving equipment, transportation equipment, . . . Etc. 

1. A hydraulic positive displacement pump with a pumping group comprising of a cam completely encircled by followers to form an enclosed chamber
 2. A pumping group according to claim 1 in which the followers rise and fall during cam rotation. 3 (currently amended) A pumping group according to claim 1 in which the volume of the enclosed chamber increases and such liquid during the followers rise.
 4. A pumping group according to claim 1 in which the volume of the enclosed chamber decreases and discharges the liquid to the pump delivery line during the followers fall.
 5. A pumping group according to claim 1 as on item 1 and with the followers rise by means of the action of the cam.
 6. A pumping group according to claim 1 with the followers fall by the action of pressurized control fluid, springs, mechanisms, or any combination of these means.
 7. A pump according to claim 1 further including a plurality of pumping groups.
 8. A pump according to claim 1 where the pressurized control fluid is provided internally or from out sources.
 9. A pump according to claim 1 with rigid or flexible followers.
 10. A pump according to claim 1 with rigid followers distributed around the cam, and each follower slides with respect to the adjacent components.
 11. A pump according to claim 1 in which buckets could be formed between the adjacent followers and components.
 12. A pump according to claim 1 in which the buckets may be governed by guides.
 13. A pump according to claim 1 with the follower sliding motion can be governed by guides.
 14. A pump according to claim 13 with the guide having cylindrical shape or else.
 15. A pump according to claim 14 with the guides having lips or else for sealing purposes.
 16. A pump according to claim 1 wherein the with the flexible followers made of one or more pieces.
 17. A pump according to claim 1 with each cam has one or more rises per one drive shaft revolution.
 18. A pump according to claim 1 where the cam push the followers directly or through rollers or pads or else.
 19. A pump according to claim 1 with rollers may have their own separation bearings.
 20. A pump according to claim 18 with rollers running over bridges in the separation zones between the followers or followers segments.
 21. A pump according to claim 1 with the followers of a pumping group while rising during suction sweep control liquid in a control chamber behind the followers.
 22. A pump according to claim 21 where the swept, pressurized control liquid can be stored under pressure. 23-24. (canceled) 